Reference — Lab
Complete Blood Count (CBC) Reference
WBC, RBC, hemoglobin, hematocrit, MCV, platelets, and differential — normal ranges, clinical significance, causes of abnormalities, and nursing implications.
Educational use only. Reference ranges vary by laboratory and patient population (age, sex, altitude). Always use your institution's reference values and clinical context for interpretation. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
CBC Components
| Test | Normal Range | Low (↓) Causes | High (↑) Causes | Nursing Implications |
|---|---|---|---|---|
| WBC (White Blood Cells) | 4,500–11,000 cells/μL | Leukopenia — viral infections, bone marrow suppression, chemotherapy, aplastic anemia, autoimmune disease | Leukocytosis — bacterial infection (most common), inflammation, stress response, leukemia, steroid use | Neutropenic precautions for WBC < 1,000; reverse isolation; report fever ≥ 38°C (100.4°F) in immunocompromised patients immediately |
| RBC (Red Blood Cells) | 4.5–5.5 million/μL (M); 4.0–5.0 million/μL (F) | Anemia — blood loss, iron deficiency, B12/folate deficiency, chronic disease, hemolysis, bone marrow suppression | Polycythemia — dehydration (spurious), COPD (secondary polycythemia), polycythemia vera | Correlate with Hgb and Hct; assess for symptoms (fatigue, pallor, dyspnea); note MCV for anemia type |
| Hemoglobin (Hgb) | 13.5–17.5 g/dL (M); 12.0–15.5 g/dL (F) | Anemia — iron deficiency (most common), blood loss, chronic disease, sickle cell, thalassemia | Polycythemia, dehydration (hemoconcentration), chronic hypoxia | Symptomatic at different thresholds — active cardiac disease → transfuse at ≤ 8 g/dL; most patients at ≤ 7 g/dL; assess orthostatic vitals, activity tolerance, pallor |
| Hematocrit (Hct) | 41–53% (M); 36–46% (F) | Anemia, overhydration (hemodilution) | Dehydration, polycythemia — Hct > 60% increases viscosity and clot risk | Hct approximately 3× the Hgb value (rule of thumb); hemoconcentrated patients need fluid resuscitation assessment |
| MCV (Mean Corpuscular Volume) | 80–100 fL | Microcytic anemia — iron deficiency (most common), thalassemia, chronic disease, sideroblastic anemia | Macrocytic anemia — B12 deficiency, folate deficiency, alcoholism, hypothyroidism, liver disease, methotrexate | MCV classifies the anemia type: microcytic = low MCV; normocytic = normal MCV; macrocytic = high MCV — guides further workup |
| Platelets | 150,000–400,000/μL | Thrombocytopenia — ITP (autoimmune), heparin-induced (HIT), DIC, TTP, chemotherapy, bone marrow suppression, hypersplenism | Thrombocytosis — iron deficiency, infection, inflammation, splenectomy, essential thrombocythemia | Bleeding precautions at < 50,000; spontaneous bleeding risk at < 20,000; hold invasive procedures at < 50,000; HIT → stop all heparin immediately |
WBC Differential
| Cell Type | Normal % | Clinical Significance | Nursing Note |
|---|---|---|---|
| Neutrophils (segs/bands) | 55–70% (segs); bands < 5% | Primary bacterial defense; elevated in bacterial infection, steroids; decreased in chemotherapy, viral infections, aplastic anemia | Left shift (increased bands) = immature neutrophils = serious infection. Absolute Neutrophil Count (ANC) = total WBC × % neutrophils — ANC < 500 = severe neutropenia |
| Lymphocytes | 20–40% | Viral immunity; elevated in viral infections, lymphoma, CLL; decreased in HIV, corticosteroids, immunosuppression | Markedly elevated lymphocytes with atypical cells = suspected lymphoma or lymphocytic leukemia |
| Monocytes | 2–8% | Phagocytosis and antigen presentation; elevated in chronic infections (TB, fungal), autoimmune diseases, monocytic leukemia | Monocytosis often indicates chronic infection — assess for TB exposure, fungal infections |
| Eosinophils | 1–4% | Elevated in allergic reactions, asthma, parasitic infections, drug hypersensitivity, Addison's disease | Eosinophilia with respiratory symptoms = consider asthma or hypersensitivity pneumonitis |
| Basophils | 0.5–1% | Rarely elevated; basophilia occurs in allergic reactions and myeloproliferative disorders | Rarely clinically significant in isolation |
Anemia Classification by MCV
| Type | MCV | Common Causes | Key Feature |
|---|---|---|---|
| Microcytic | < 80 fL | Iron deficiency (most common), thalassemia, chronic disease, sideroblastic anemia | Small, pale RBCs; low ferritin with iron deficiency |
| Normocytic | 80–100 fL | Acute blood loss, hemolysis, anemia of chronic disease (early), aplastic anemia, renal failure (EPO deficiency) | Normal-sized RBCs; broad differential — use reticulocyte count to differentiate |
| Macrocytic | > 100 fL | B12 deficiency (pernicious anemia, veganism), folate deficiency, alcoholism, liver disease, hypothyroidism, methotrexate, hydroxyurea | Large RBCs; B12 deficiency causes neurological symptoms (paresthesias, ataxia) |
NCLEX Focus Points
Left shift: Increased band neutrophils = immature cells being released = severe infection. A left shift is more clinically significant than the total WBC count.
ANC calculation: ANC = WBC × % neutrophils (segs + bands). ANC < 500/μL = severe neutropenia — implement neutropenic precautions.
HIT (Heparin-Induced Thrombocytopenia): Platelet drop of > 50% from baseline occurring 5–14 days after heparin exposure. STOP all heparin (including flushes). Switch to alternative anticoagulant (argatroban, bivalirudin). Paradoxically causes thrombosis despite low platelets.
Sickle cell crisis: Hydroxyurea increases fetal hemoglobin (HbF) which inhibits sickling — associated with macrocytosis as a therapeutic side effect.
Pernicious anemia: B12 deficiency due to lack of intrinsic factor (autoimmune or post-gastrectomy) — treated with IM or high-dose PO B12, not dietary supplementation alone (cannot absorb without intrinsic factor).
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with Standard laboratory reference ranges · Clinical & Laboratory Standards Institute (CLSI). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →